The X-ray tube has become essential in medical diagnostic imaging, medical therapy, and various medical testing and material analysis industries. Typical X-ray tubes are built with a rotating anode structure for the purpose of distributing the heat generated at the focal spot. The anode is rotated by an induction motor consisting of a cylindrical rotor built into a cantilevered axle that supports the disc shaped anode target, and an iron stator structure with copper windings that surrounds the elongated neck of the X-ray tube that contains the rotor. The rotor of the rotating anode assembly being driven by the stator which surrounds the rotor of the anode assembly is at anodic potential while the stator is referenced electrically to ground. The X-ray tube cathode provides a focused electron beam which is accelerated across the anode-to-cathode vacuum gap and produces X-rays upon impact with the anode.
In an X-ray tube device with a rotatable anode, the target consists of a disk made of a refractory metal such as tungsten, and the X-rays are generated by making the electron beam collide with this target, while the target is being rotated at high speed. Rotation of the target is achieved by driving the rotor provided on a support shaft extending from the target.
Some X-ray tubes are turned on and off at a rapid rate as a part of their task, such as for diagnostic imaging, or any applications where it is desired to review a particular activity which is cyclic in nature. It is customary in such circumstances to provide a costly grid control power supply as a means of switching power ("mA", i.e., current) on and off, for bursts of X-ray. This power supply, or "grid tank", supplies a negative referenced switched voltage to the structure surrounding the filament known as the cathode cup. When the cathode cup or grid is substantially negative with respect to the thermionic emitter (i.e. filament), the surrounding electrode cloud is prevented from flowing to the anode and the tube is said to be "cut off" or "grided off" Our invention makes improved use of the cathode power supply and the normal distributed capacity, which is a part of the physical structures in an X-ray tube and the X-ray's tubes connecting wires, to provide a less costly, more reliable form of "mA" (current) switching. The grid power supply or "Grid Tank" is completely eliminated.
It would be desirable then to have improved use of the cathode power supply and the normal distributed capacity, to provide a less costly, more reliable form of "mA" switching.